The jet stream is a 250 mph river of wind
Bands of fast wind high in the atmosphere steer storms and shave time off transatlantic flights.
Jet streams are narrow ribbons of high-speed wind that snake around the planet about five to nine miles (roughly 8–14 km) up, near the top of the troposphere.
NOAA notes they average around 110 mph but can blast past 250 mph — fastest in the polar jet during winter. They form where warm and cold air masses collide: the bigger the temperature contrast, the stronger the wind, as Encyclopædia Britannica explains.
That is why they matter far below. Jet streams steer weather systems and dictate where storms track, and aircraft ride them eastward to save fuel and time while avoiding them on the return leg.
A west-to-east tailwind can trim an hour or more off a transatlantic crossing.
Sources & references
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